DESCRIPTION: (adapted from the investigators abstract) Inactivation of tumor suppressor genes plays a causal role in the dlevelopment of human cancers. Deleted in Colorectal Cancer [DCC] gene is a putative tumor suppressor gene. Deduced amino acid sequences show a high homology with cell adhesion molecules of the Ig superfamily. Loss of heterozygosity and/or loss of DCC expression have been observed in many human cancers, indicating that inactivation of the DCC gene may contribute to cancer development. Although DCC was identified in 1990, its function is still largely unknown. In their preliminary studies, the investigators found that DCC expression induced apoptosis or G2/M cell cycle arrest of tumor cells. Caspase-3 was activated and the poly (ADP-ribose) polymerase, a substrate of caspase-3, was cleaved in cell lines that undergo apoptosis. In cell lines that arrested at the G2/M by DCC, CdkI activity was inhibited. Using the interaction trap yeast two-hybrid system, they found that reaper, sina, FKBP12 and six new proteins (dubbed DIP) interact with the DCC cytoplasmic domain. Reaper is an activator of apoptosis in Drosophila, and it shares homology with the death domain identified in mammalian death signaling molecules FADD, TRADD and RIP. FKBP12 is a prolyl isomerase that binds to immunosuppressant drug FK506 and rapamycin and is involved in cell cycle arrest and/or apoptosis. Sina targets the DCC protein to ubiquitin-proteasome for degradation. The function of DIPs is currently unknown. In this proposal, the signaling mechanism of DCC-induced apoptosis will be investigated. They hypothesize that the cytoplasmic domain of DCC transduces a signal resulting in activation of caspases which triggers apoptosis. The apoptotic signal of DCC is mediated by protein(s) that interact(s) with the DCC cytoplasmic domain. To test this hypothesis, they propose to 1) Map the region(s) in the DCC cytoplasmic domain required for inducing apoptosis by domain deletion and analysis of tumor-derived mutants; 2) Identify candidate mediator(s) of DCC apoptotic signal by analysis of DCC/interactor protein binding and the DCC apoptotic activity; 3) Determine whether inhibition of caspase-3 can block DCC-induced apoptosis, and whether inhibition of initiator caspases such as caspase-8 and -10 can abrogate the DCC-induced apoptosis.